Background: AFM24 is a tetravalent, bispecific innate cell engager that binds EGFR on solid tumors and CD16A on natural killer (NK) cells. AFM24 redirects NK cells to EGFR-expressing (EGFR⁺) solid tumors, enhancing antibody-dependent cellular cytotoxicity. AFM24 induced lysis of EGFR⁺ tumor cell lines in vitro independent of EGFR expression level and mutation status. The dose escalation phase (Phase 1) of the presented study (NCT04259450) previously established the recommended Phase 2 dose at 480 mg based on tolerability, receptor occupancy, and pharmacokinetics. Correlative science data revealed an activation and enrichment of immune cells in the tumor microenvironment. Here we present preliminary data from the Phase 2a CRC expansion cohort. Methods: The Phase 2a expansion phase is evaluating 480 mg AFM24 in patients with histologically or cytologically confirmed microsatellite stable, RAS wild type EGFR⁺ CRC. Patients have relapsed or refractory disease to ≥2 prior lines of therapy including an EGFR targeted therapy. EGFR⁺ is defined as positive staining for EGFR in ≥1% of tumor cells per local immunohistochemistry assay. The study follows Simon’s two-stage design. The primary endpoint is the overall response rate per RECIST v1.1 by investigator assessment; secondary endpoints include safety and tolerability; efficacy per iRECIST is exploratory. AFM24 is administered intravenously once weekly in a 28-day cycle. Tumor assessments are performed at screening, cycles 2, 4, 6, 8, and every 3 cycles thereafter. Results: As of December 2022, 16 patients with Stage 4 CRC were enrolled and treated with 480 mg AFM24 in the study. The median (range) age was 66 years (51–77); 11 males and 5 females; 9 Asian, 7 White). The median number of prior therapies was 4 (2–7) and the median treatment duration was 5.1 weeks (1.0–22.0). Treatment-related adverse events (TRAEs) were reported in 14/16 patients; infusion-related reactions (IRRs, 12), pruritus (3), lymphopenia (3), and anemia (2) were the most common. AFM24 TRAEs of Grade ≥3 occurred in 6 patients and included lymphopenia (3), decreased neutrophil count (1), increased blood bilirubin (1) and IRRs (1). To date, no objective responses were observed. Seven patients remain on treatment including 1 patient with confirmed stable disease ongoing for 5 months exhibiting a tumor reduction of –17%. Final interim results will be presented. Conclusions: The novel mechanism of action of AFM24 may provide an alternative treatment approach for patients with EGFR⁺ solid tumors. In this study, AFM24 monotherapy was adequately tolerated in a heavily pretreated population of patients with EGFR⁺ CRC. AFM24 is also being investigated in combination with atezolizumab and autologous NK cells in various EGFR⁺ solid tumors. Clinical trial information: NCT04259450.